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Chapter 2: 16 PE (page 82)
A cheetah can accelerate from rest to a speed of 30.0 m/s in 7.00 s. What is its acceleration?
The acceleration of the cheetah is 4.28 m/s2.
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a) Calculate the height of a cliff if it takes\({\bf{2}}.{\bf{35}}{\rm{ }}{\bf{s}}.\)for a rock to hit the ground when it is thrown straight up from the cliff with an initial velocity of\({\bf{8}}.{\bf{00}}{\rm{ }}{\bf{m}}/{\bf{s}}\). (b) How long would it take to reach the ground if it is thrown straight down with the same speed?
A woodpecker鈥檚 brain is specially protected from large decelerations by tendon-like attachments inside the skull. While pecking on a tree, the woodpecker鈥檚 head comes to a stop from an initial velocity of 0.600 m/sin a distance of only 2.99 mm.
(a) Find the acceleration in m/s2 and in multiples of (g = 9.80 m/s2).
(b) Calculate the stopping time.
(c) The tendons cradling the brain stretch, making its stopping distance 4.50(greater than the head and, hence, less deceleration of the brain). What is the brain鈥檚 deceleration, expressed in multiples of g?
Suppose you throw a rock nearly straight up at a coconut in a palm tree, and the rock misses on the way up but hits the coconut on the way down. Neglecting air resistance, how does the speed of the rock when it hits the coconut on the way down compare with what it would have been if it had hit the coconut on the way up? Is it more likely to dislodge the coconut on the way up or down? Explain.
A soft tennis ball is dropped onto a hard floor from a height of \[{\bf{1}}.{\bf{50}}{\rm{ }}{\bf{m}}\]and rebounds to a height of\[{\bf{1}}.{\bf{10}}{\rm{ }}{\bf{m}}\]. (a) Calculate its velocity just before it strikes the floor. (b) Calculate its velocity just after it leaves the floor on its way back up. (c) Calculate its acceleration during contact with the floor if that contact lasts\[{\bf{3}}.{\bf{50}}{\rm{ }}{\bf{ms}}{\rm{ }}\left( {{\bf{3}}.{\bf{50}} \times {\bf{1}}{{\bf{0}}^{ - {\bf{3}}}}{\bf{s}}} \right)\]. (d) How much did the ball compress during its collision with the floor, assuming the floor is absolutely rigid?
A basketball referee tosses the ball straight up for the starting tip-off. At what velocity must a basketball player leave the ground to rise above the floor in an attempt to get the ball?
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